Make backend port configurable via .env and update related configurations

tests/core/test_config.py

@@ -0,0 +1,13 @@
+from app.core.config import Settings
+
+
+def test_settings_default_backend_port_is_8000():
+    settings = Settings(datamall_api_key="test-account-key")
+
+    assert settings.app_port == 8000
+
+
+def test_settings_reads_backend_port_from_env_value():
+    settings = Settings(datamall_api_key="test-account-key", app_port=9010)
+
+    assert settings.app_port == 9010